NCO自由基与H反应的机理和动力学

研究采用密度泛函理论中的B3LYP方法,在6-311G(d,p)基组水平下,优化反应物、产物、中间异构体和过渡态分子,得到可靠的几何构型和频率.通过内禀反应坐标计算,确认了四条反应通道,并且以通道中中间体、过渡态相对能量为基础,讨论了各反应通道的优先顺序.在反应中,H和NCO的初始连接有两种方式,H分别进攻NCO两端的N和O,进行无势垒加合,得到两个低能中间体HNCO和HOCN.HNCO中∠NCO从172.9°减小到69.0°,生成一个相对能量较高但N—C键较长的中间体,该中间体发生N—C键断裂生成主要产物P1(CO+NH).从HNCO和HOCN出发均可生成次要产物P2(CN+OH),而从HNCO出发还有另一条生成产物P3(CH+NO)的路径,反应沿该路径进行的可能性较小.

Mechanism and Kinetics of NCO+H Reaction

The potential energy surface of radical-radical reaction between NCO and H was investigated theoretically with the density function theory and ab initio method at CCSD（T） /6--311G （d, p） //B3LYP/6--311G（d, p） level. Based on the calculations of intrinsic reaction coordinates, four reactive paths were confirmed. And then, the main reaction path was discussed based on the relative energies of isomers and transition states. The mechanism of the reaction has two initial association ways. The H atom attacks initially to N atom and O atom of NCO to form two initial isomers of HNCO and HOCN, respectively. From HNCO, the most dominated production of P1 （CO＋NH） is produced. The minor production of P2 （CNq-OH） can be obtained from either HNCO or HOCN. The product of P3 （CH＋NO） is less favorable.